The present invention relates generally to atmospheric models of optical turbulence and more specifically to an application of a mathematical equation that can be programmed into a computer which converts the usual radiosonde data (weather balloon) to the optical turbulence parameter, Cn2. It can also be programmed into a weather forecasting model to forecast optical turbulence. The latter will be used by the Air Force in order to serve as an electronic decision aid so that, for example, one can position the Airborne Laser (ABL) weapon in a location which will, on a given day, have a minimum of turbulence between weapon and the theater missile target. (The presence of too much turbulence can degrade weapon effectiveness.)
As the acquisition of accurate knowledge of meteorologic conditions in the upper atmosphere has become increasingly important, devices have been developed to satisfy these requirements. As a result of the availability of this data, meteorologists are better able to make their predictions of future weather conditions.
One such atmospheric meteorological sensing and telemetering system is described in U.S. Pat. No. 3,781,715 by Poppe et al, the disclosure of which is incorporated herein by reference. The Poppe radiosonde includes a number of meteorological parameter sensors, which are generally of the type having an electrical parameter, e.g., resistance, which is proportional to the sensed meteorological parameters, e.g., temperature. The sensor is connected as part of a meteorological data generator, which produces a signal utilized to modulate a carrier signal. The thus modulated carrier is thereafter transmitted by a suitable antenna carried by the radiosonde and received and processed at a remote, ground-based weather tracking station.
For the information transmitted by the weather radiosonde to be most meaningful, it must be correlated to meteorological data.
Currently, models are needed to convert standard meteorological data into vertical profiles of Cn2, the structure constant for optical index of refraction fluctuations. Profiles of Cn2 from the ground to 20 or 30 km are needed to ascertain the effects of turbulence on laser beam propagation from ground to space as well as on light propagation from space to ground. Such information would be available in large quantities if radiosonde information could be converted to Cn2 profiles. Such information could then be used for assigning design parameters for adaptive optical systems, which can greatly reduce the effect of turbulence. When the Cn2 model is incorporated into a three-dimensional forecast model (or electronic decision aid) then it will be possible to calculate the effects of turbulence on air to air propagation geometry as will be the case for the ABL and the theater missile target.
This discussion describes our radiosonde Cn2 model and tests of it. Note that this model does not relate to the convective boundary layer and our tests will be applied with this in mind. Other models exist for the boundary layer and these would be added, for example, when parameters such as ro the coherence length, are estimated because ro is sensitive to near-ground Cn2. In this report we will only consider parameters sensitive to Cn2 above the boundary layer.
This invention description describes how the AFGL model was created from very high resolution velocity profiles that we obtained in the stratosphere by means of rocket laid smoke trails; next it will explain how the resulting model is used to convert radiosonde data into Cn2 profiles. Then, comparisons between model and thermosonde profiles of Cn2 will be made.
At the end of the discussion some comments will be made about the lessons we learned in this research. Suggestions for future research will also be offered.
The present invention is an application of a mathematical equation that can be programmed into a computer, which converts the usual radiosonde data (weather balloon), to the optical turbulence parameter, Cn2. It can also be programmed into a weather forecasting model to forecast optical turbulence. The structure constant, Cn2, for optical index of refraction fluctuations is the key to the design of adaptive optical systems that minimize the effects of turbulence on laser beam propagation. This invention uses our model, which converts standard radiosonde data into Cn2 profiles. The results are compared to directly measured in situ values of Cn2 obtained by means of balloon borne thermosondes.
The present invention may be defined as a process for estimating optical turbulence Cn2 using either radiosonde data or data contained within a weather forecasting computer model. The process includes the steps of:
collecting radiosonde data for an area of interest, the radiosonde data including measurements of:
absolute temperature in degrees K (xc2x0K), pressure (P) in mB, dry adiabatic lapse rate (xcex3) winds (n/s) and a measure of height above ground in meters(m); (or, alternatively, these data in a weather forecast model)
determining an estimate of the largest scale of inertial range turbulence(L); and calculating an estimate for the optical turbulence from the radiosonde data and from L.
In the process of the invention the calculating step is performed by
Cn2=2.8M2 L4/3 
where:       M    2    =            [                        (                                    79              xc3x97                              10                                  -                  6                                            ⁢              P                                      T              2                                )                ⁢                  (                                                    ⅆ                T                                            ⅆ                z                                      +            γ                    )                    ]        2  
and where T is absolute atmospheric temperature in xc2x0K, P is pressure in mb, xcex3 is the dry adiabatic lapse rate of 9.8xc3x9710xe2x88x923 xc2x0K/m, and z is the height above ground.
The innovative feature of the invention includes the estimate of L, the scale of inertial range turbulence from radiosonde data or from computer weather forecast data, as discussed below.